knockout.js, jquery, and tastypie: Automattically perform a "PUT" to your model's resource_uri when certain observables change value

example.js

    // usage inside a vm:
    var fooVM = function(){
        var self = this;
        var resource_uri = ko.observable('/api/v1/foo/');
        var bar = ko.observable(1);
        var baz = ko.observable(1);
        ko.saveOnChange(self,['bar']);
    }
    var f = new fooVM();
    f.bar(2);  // causes a PUT to /api/v1/foo/
    f.baz(2);  // doesn't do anything

saveOnChange.ko.js

    // provided an instance of a vm and an array of observable names within it
    // will subscribe to changes, and kick off an ajax PUT to the vm.resource_uri value
    // tries to autodetect use of ko.mapping vs standard ko for the toJS conversion

    ko.saveOnChange = function(vm,observables,uri,method,pre_save_fn,post_save_fn){
        vm._saving                  = ko.observable(false);
        vm._last_saved              = ko.observable(null);
        vm._save_on_change_uri      = uri;
        vm._save_on_change_method   = method || 'PUT';
        vm._pre_save_fn             = pre_save_fn;
        vm._post_save_fn            = post_save_fn;

        // delay activating this because
        setTimeout(_.bind(function(vm,observables){
            var self = this;
            self.vm  = vm;
            self.vm._save_on_change_uri  = self.vm._save_on_change_uri || self.vm.resource_uri();
            // console.log('attaching to',self.vm.id(),observables);
            ko.utils.arrayForEach(observables, function(o) {
                var ob = self.vm[o];
                if (ko.isObservable(ob)){
                    // TODO: how do we remove this bind function to avoid lodash/underscore?
                    ob.subscribe(_.bind(function(vm,val){
                        if (vm._pre_save_fn){
                            vm._pre_save_fn(vm);
                        }
                        vm._saving(true);
                        var toJS = (vm.__ko_mapping__ && ko.mapping)?ko.mapping.toJS:ko.toJS();
                        vm._saving(true);
                        $.ajax({
                            type          : vm._save_on_change_method
                            , url         : vm._save_on_change_uri
                            , data        : JSON.stringify(toJS(vm))
                            , processData : false
                            , dataType    : "json"
                            , contentType : "application/json"
                            , success    : function(data){
                                vm._saving(false);
                                vm._last_saved((new Date()));
                                if (vm._post_save_fn){
                                    vm._post_save_fn(vm,data);
                                }
                                // console.log('save response :',data);
                            }
                        });
                    },this,self.vm));
                }else{
                    console.error('ERROR: ko.saveOnChange() -- "' + ob + '" is not a ko.observable');
                }
            });
        },this,vm,observables),5);
    };